Generally, a system for driving a motor includes a power storage device (e.g., a battery), an inverter for converting direct current (DC) power, which is stored in the power storage device, into alternating current (AC) power for driving a motor, and the motor.
Here, the inverter may include a plurality of switching elements, and the plurality of switching elements may be controlled by a pulse width modulation (PWM) method to generate the AC power. The AC power generated by the inverter is supplied to the motor and thus the motor is driven.
Various methods are known as a PWM method for controlling switching elements in an inverter, and recently, a space vector PWM (SVPWM) has been widely applied in the industry. According to the SVPWM, a vector [000] and a vector [111], which are invalid vectors, have the same magnitude, and a valid vector and an invalid vector alternately appear twice during a single switching cycle and thus a motor ripple has twice a switching frequency. Further, since the invalid vectors [000] and [111] are used, all switches perform an ON/OFF operation once. Owing to the above-described features, the SVPWM has a disadvantage in that the number of switching times is increased to cause a switching loss.
A discontinuous PWM (DPWM) method is known as one of alternative PWM methods for reducing a switching loss generated in the SVPWM. In the DPWM method, since a single switch does not perform ON/OFF operations during a single switching cycle, an actual number of switching times is reduced to ⅔ of the number of switching times in the SVPWM method.
However, since a valid vector and an invalid vector appear once per switching cycle, there is a disadvantage in that a motor current ripple becomes equal to a switching frequency such that a magnitude of the motor current ripple becomes larger than that of the SVPWM. That is, in consideration of the same current ripple, using the SVPWM may reduce the number of switching times. Therefore, in the present industry, the SVPWM method is widely used for inverter switching control.
There is a need in the art for a new pulse width modulation technique which can overcome disadvantages of the SVPWM method in which an inverter loss is increased due to an increase in number of switching times and the DPWM method in which a current ripple is increased.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.